Moving Air

The Science of Air and Temperature

In this activity, students observed the following properties of air.

Temperature determines how much the molecules in air move. The molecules in air (and in all gases) are constantly moving in a random motion. As temperature rises, molecules become more active. They bounce off one another and off the sides of a container with more energy. At lower temperatures, there is less motion and energy among molecules.

Temperature determines how much space air occupies. Gases take up space, but unlike liquids or solids, they have no definite shape or volume unless they are put into a container. The amount of space occupied by a gas is determined by temperature. For example, an increase in temperature causes air to expand and rise (due to more energetic “bouncing” of air molecules). A decrease in temperature will cause air to contract (take up less space), and sink.

Temperature changes account for most air movement that we can observe, both indoors and outdoors. In a room with areas of different temperatures, air currents will develop as higher-energy (“bouncier”) warm air rises and lower-energy cool air sinks. For example, consider the following situations.

Opening the freezer or refrigerator door allows cold air to escape and travel down to the floor.

A bedroom upstairs is warmer than the bedroom below it because warm air rises.

A hot air balloon rises because hot air inside the balloon lifts it off the ground. In the infrared image on this slide, pink indicates very hot air temperatures inside the balloon; blue indicates cooler air. Notice that the hottest air is at the very top of the balloon, while the cooler air is at the bottom.